The conventional method of reducing a biological wasted sludge involves the use of aerobic or anaerobic digestion by which the nature of the biological wasted sludge is stabilized. Meanwhile, the sludge dehydration is enhanced. In light of the biological wasted sludge being a solid, the conversion of the biological wasted sludge by a biological digestive process into a biologically usable aqueous solution is a time-consuming process. For this reason, the biological wasted sludge is first treated with a physical or chemical hydrolysis before they are subjected to the aerobic or anaerobic digestion, so as to speed up the hydrolysis of the biological wasted sludge. However, in the wake of the hydrolysis of the biological wasted sludge, a portion of the biological wasted sludge can be further hydrolyzed and decomposed, with a certain proportion thereof incapable of being further decomposed. The non-decomposed portion of the hydrolyzed sludge is formed of minute particles, which are similar in density to water and are therefore susceptible to loss along with the treated water in a biological treatment system, thereby resulting in deterioration in quality of an effluent.
In spite of the fact that the conventional method described above is capable of attaining the stabilization of the nature of the biological wasted sludge and the enhancement of the dehydration of the biological wasted sludge, the conventional method is in fact ineffective in reducing the biological wasted sludge, with its effectiveness ranging from 5 to 10%. The hydraulic residence time (HRT) of the aerobic digestion of the conventional sludge digestive system lasts for 20–30 days as compared with 30 days or more for the anaerobic digestion. For this reason, the conventional method calls for the use of a large reactor in conjunction with a high temperature digestive system. It is therefore readily apparent that the conventional method is not cost-effective.